Ability to specify which classes should not be removed, like "preheader"

[TopCoder02]

You can read more about preheaders here : https://www.campaignmonitor.com/blog/email-marketing/a-practical-guide-to-email-preheaders/

StripeIDandClassAttributes (it's all or nothing) But you should be able to prevent the removal of the preheader class. Since this library pertains to making the HTML email friendly.